The present invention relates to digital transmission technology and, in particular, to transmission concepts particularly well suited for time-varying transmission channels as may be encountered in mobile radio and broadcasting, and wherein several data types (e.g. audio, video) are to be transmitted via a single signal.
Time and/or frequency interleaving, combined with so-called forward error correction methods (FEC methods), is part of a basic principle in transmission technology. Such interleaving is also employed in digital video broadcasting (DVB), for example. A relatively new transmission standard among the DVB family with which digital broadcasting programs may be received via small and/or mobile devices is digital video broadcasting via satellite for handheld devices, DVB-SH for short (Digital Video Broadcasting—Satellite services to Handheld devices).
DVB-SH uses a 3GPP2 turbo encoder (3GPP2=3rd Generation Partnership Project 2) as the channel encoder. This turbo encoder has an information word of the size Ltc-input supplied to it (for DVB-SH: Ltc-input=12,282 bits). After encoding the information words, the turbo encoder outputs code words at a predefined code rate CR. Even though for DVB-SH, fundamentally there are different code rates of from 1/5 to 2/3, it is currently possible for DVB-SH to set only one single code rate for all of the information words for one signal. Thus, all of the code words output by the encoder are equally sized, having a size of Ltc-output=(Ltc-input+6)/CR.
Subsequently, the code words are subjected to bit-wise interleaving and subdivided into so-called interleaver units (IUs). For DVB-SH, the size of the individual interleaver units amounts to 126 bits in each case, which result from puncturing 2 bits among 128 bits, respectively, of the bit-interleaved code word. The interleaver units (IUs) of a code word are sorted into groups of 48 IUs. This is schematically depicted in FIG. 1.
A code rate CR=2/3 and an info word length Ltc-input=12,282 bits result in a code word length Ltc-output=18,144 bits, which corresponds to 144 interleaver units per code word. The interleaver units of a code word are sorted into groups of 48 IUs, which in the example presented here results in 144/48=3 groups. As is shown in FIG. 1, the IUs of the individual groups are arranged in a column-wise manner, so that a 48×3 IU matrix results. In FIG. 1, the individual IUs are labeled C, R, C meaning the column and R meaning the row of the IUs in the respective code word. For DVB-SH, the allowed code rates and IU sizes have been selected such that the code words fill up entire columns (FIG. 1: code rate 2/3 corresponds to three columns). Consecutive code words are sorted in consecutive columns, as has just been described.
Subsequently, the columns of the IU matrix are fed into an interleaver means 10, in particular into a convolutional interleaver means, one by one, which means comprises, in accordance with the 48 interleaver units, N=48 delay means, which will also be depicted as delay lines below for the purpose of clarity. For example, the delay means might be realized by means of an addressable (RAM) memory. I.e., the 0th IU of a column ends up in the 0th delay means or delay line (D=0), the 1st IU of a column ends up in the 1st delay line (D=1), etc., i.e. D=0, . . . , N−1. A delay means or delay line, e.g. in the form of a so-called tapped delay line, is some kind of shift register, wherein each register stage may store an entire IU, i.e., e.g., 126 bits, at once, which is then forwarded to the next stage as a block during shifting. Between each shifting operation, a new column of a code word is started at the input of the interleaver means 10, and accordingly, N=48 interleaved IUs are read at the output of the N=48 delay lines, i.e. at the output of the interleaver means 10. Such a write and/or read operation is referred to as an interleaver cycle. A delay of an interleaver unit, or IU, via a delay line is therefore an integer multiple of an interleaver cycle.
FIG. 2 shows the fundamental structure of a convolutional interleaver means 10, or a convolutional interleaver, as is employed, in a slightly modified form, for DVB-SH. Only the principle is to be explained below. For specific implementation details, please refer to the corresponding DVB-SH standardization documents.
The convolutional interleaver 10 comprises N=48 parallel delay lines 12. The lines 12 are fed, one by one, by an input coupler in the form of a demultiplexer 11 (DEMUX). It shall be mentioned at this point that the input coupler 11 and further couplers described below are depicted as (de)multiplexers only for clarity's sake. However, the couplers might also be realized by memory controllers and/or address generators for addressing a RAM memory, for example. The input of the demultiplexer 11 is coupled to the previously described bit interleaver (not shown). The demultiplexer 11 feeds every delay line 12 with exactly one interleaver unit (IU), which comprises, by way of example, 126 code bits, or symbols. Then the demultiplexer 11 switches to the next line 12, etc. At the beginning of a new column, the demultiplexer switches to the first line 12a. The end of a column is reached once the demultiplexer 11 has fed an IU into the last line (index N−1).
The convolutional interleaver 10 may be configured within a certain range of possibilities. Each delay line may comprise different and different numbers of delay elements (E=early part, M=middle part, L=late part), so that the delay may be different for each delay line 12.
Specifically, the convolutional interleaver 10 depicted in FIG. 2 comprises the input coupler 11, which is configured as a demultiplexer and is referred to as DEMUX in FIG. 2. In addition, there is an output coupler 12, which is configured as a multiplexer and is referred to as MUX in FIG. 2. A plurality of delay lines 12 are arranged between the two multiplexers 11 and 14, which delay lines are subdivided into three groups in the interleaver shown in FIG. 2. The first group is referred to as the early part 12d. The second group is referred to as the middle part 12e, and the third group is referred to as the late part 12f. 
Each delay line, or interconnect line, except for the first interconnect line 12a, exhibits a specific delay, it being possible, however, for the delay lines to be configured differently within the three groups. In addition, FIG. 2 shows that the delay increases by one increment (E, M or L) from delay line (tap) to delay line in each case, so that, e.g., the interconnect line tap (middleStart-1) has a number of tap (middleStart-1) delay elements E. In addition, each delay line of the second group 12e has the same number of delay units E as the last delay line of the first group 12d and, additionally, a number of M delay elements that increases from delay line to delay line. Accordingly, each interconnect line of the late group 12f also has the same number of E delays as the last interconnect line of the first group 12d, and the same number of M delays as the last delay line of the second group 12e, as well as a number of L delay elements that increases from delay line to delay line. Please see patent document DE 10 2006 026 895 B3 for further details. The individual delays of the three groups 12d, 12e, 12f in combination represent an interleaver specification, or interleaver configuration.
The time passing between input and output may be different for each delay line of the convolutional interleaver means 10. This is why the N=48 IUs read out within one interleaver cycle do not belong to one single code word, but are a mixture of IUs of different code words (and are therefore interleaved). For the current DVB-SH standard, there are basically many different interleaver configurations, but currently only one single interleaver configuration, or interleaver specification, may be used for all of the info/code words within a signal.
With reference to FIG. 1, the N=48 IUs read out from the interleaver means 10 are now transmitted in a time-sequential manner. The next N=48 IUs that are read out are attached in accordance with their delays D(0 . . . 47). In the example of FIG. 1, a next transmission transmission frame (frame) starts after 21 interleaver cycles, i.e. D=21. In total, the 144 IUs of the code word represented are transmitted within transmission frames i to i+45, i.e. within 45 transmission frames. Consequently, an overall time delay of the exemplary interleaver means 10 amounts to 45 transmission frames.
FIG. 3 shows, by way of example, how several code words CW0, CW1, CW2 and CW3, all of which have been encoded at a code rate of 2/3, are interleaved together by the interleaver means 10 and are then transmitted in a temporal manner. As may be seen, the code words CW0, CW1, CW2 and CW3 are interleaved with one another by the interleaver 10, i.e. the original sequence of interleaver units of the individual code words has been changed by the interleaver 10.
Different data need different boundary conditions for transmission. Some data, such as radio and video programs, for example, which are received by a very large number of users at the same time, has to be robust against short-term (within the range of seconds) interferences of the transmission channel. However, signal delays only play a minor role. Such data should be protected for several seconds by means of a strong channel code (low code rate) and temporal interleaving.
Other data, as come up with telephone connections, for example, need to be less robust since they are received by one single user only, but real time plays a very important part in this context. Thus, only a limited delay (e.g. smaller than 150 milliseconds) may be introduced by the interleaving. Thus, such data should be provided with a channel code of a high code rate and relatively short interleaving.
For further data, there may possibly be almost-real-time requirements (a delay of less than 1 second) and a high level of robustness (e.g. signaling information for congestion or power control of an uplink (i.e. return links) of the terminals, or for a live transmission of a soccer match). Therefore, low code rates and a medium interleaving duration should be employed for this purpose.
Some data services (e.g. software update of a navigation device) tolerate a very long delay and need to be provided with only little robust protection (an error protection code on a higher transmission layer will see to this). Accordingly, high code rates and long interleaver durations are needed for this purpose.
A multitude of other scenarios with corresponding requirements are also feasible. Such requirements are referred to as the Quality of Service (QoS) of a transport channel. Potential QoS parameters of a service include, for example:                robustness,        latency allowed,        temporal jitter,        data rate.        
Currently, DVB-SH provides only one single transport channel with one single QoS for all of the transmitted data within a physical signal, since only one single channel code and one single interleaver configuration are possible per signal.
However, it would be advantageous to have the possibility of simultaneously transmitting several transport channels having different QoS, i.e. different code rates and/or different interleaver configurations. Thus, telephone calls, for example, might also be transmitted in addition to the broadcast data originally envisaged for transmission.
Transmission of several transport channels, or so-called pipes, also takes place, for example, for ETSI SDR (European Telecommunications Standards Institute, Satellite Digital Radio), wherein entire time slots may be assigned to a first or a second transport channel in each case.
For the ETSI SDR standard, there are already several interleaver devices, or interleavers, for one single pipe (see FIG. 3 of ETSI TS 102 550 v1.3.1.) because a pipe is subdivided into time slots (however, the principle would also work, for other standards, without this subdivision into time slots). On the right-hand side in FIG. 3 of ETSI TS 102 550 v1.3.1., outputs of all of the time slot interleavers are then collected again by a so-called collector, and form a pipe. Chapter 4.9 describes that subsequently, all of the pipes are again (time-) multiplexed together. If a first pipe is to have a lower data rate, it will simply be made smaller in the time multiplex (with the SDR standard, it would be reduced by one or more time slots), and the available time (transmission resources) would be taken over by a second pipe.
The disadvantage of this approach is that it cannot be used for existing systems having a first transport channel that is read out from the output of an interleaver device within the transmitter and is then transmitted, and wherein transmission resources of the first transport channel are taken over by a second transport channel without the receiver having to be informed about this in order to de-interleave and decode the first transport channel.
There are already terminals for the current DVB-SH standard. Upgrades, or extensions, of this standard should therefore be in a backward-compatible form such that existing terminals may decode a portion of the data transmitted, specifically that portion of the data which is relevant to them. Since current terminals have been built for broadcast applications, they may represent corresponding broadcast data (e.g. audio and/or video programs). However, they currently cannot make any use of data from telephone connections, for example.